This invention relates generally to methods and systems for measuring atmospheric conditions and more particularly, to methods and systems for collecting atmospheric weather data using an aircraft.
An important obstacle to improved forecasting is lack of data about water content in the troposphere. Water content of an air mass can change rapidly during storms, over moist soil, or over bodies of water such as oceans. An inability to track changes in water content in these and other areas contributes to inaccurate weather forecasts.
Existing methods for detecting and quantifying water vapor are inadequate because they can only be implemented on a local scale over land thereby leaving vast gaps in global meteorological continuity. The largest gaps occur over oceans where most atmospheric conditions originate. Although the existing atmospheric sensing systems listed below exhibit high resolution capabilities on a local scale, it is not practical to deploy such systems on a global scale because they are expensive to implement or maintain on a global scale and they lack adequate temporal and/or spatial resolution for realistic use on a global scale.
Currently, a primary source of water vapor measurements are ground-based humidity sensors and balloon-borne sensors called “radiosondes.” Radiosonde data have high quality, but have relatively poor spatial and temporal resolution. The radiosonde, an expendable balloon-borne instrument package that relays temperature, humidity, and pressure data to a ground receiver by radio signals, is the traditional cornerstone of the worldwide operational weather analysis and prediction system through deployments twice daily at several hundred sites around the world. However, the twice daily radiosonde deployments are primarily over land and are sparsely distributed due to cost considerations. No above-ground measurements are available during intervals between launches or at locations far from radiosonde launch points. For these reasons, radiosonde data is too costly and localized to support high resolution global meteorology.
A limited number of commercial air carriers presently provide real-time wind, pressure, temperature, and humidity readings around the world as part of a system called Aeronautical Communications Addressing and Reporting System (ACARS). Although the ACARS system provides about 10,000 readings per day world wide at a cost about 100 times less than the recurring cost of radiosondes, the vast majority of ACARS readings are around airports and along common flight paths at established cruise flight levels which limits the spatial scope of this otherwise valuable data.
Earth-based Differential Absorption Lidar (DIAL) and Raman Lidar systems are used to provide wind and water vapor profiles in remote areas. However, such systems are not economic to install and maintain, they do not penetrate cloud cover, and the lasers used are highly energized and are therefore not eye-safe.
Water vapor radiometers are instruments that measure microwave energy emitted by the atmosphere to estimate zenithal integrated water vapor. Integrated water vapor is a measure of the depth of liquid water that would result if a column of water vapor were condensed into liquid water. Zenithal integrated water vapor (IWV), also known as Precipitable Water Vapor (PWV), is the integrated water vapor in a vertical column directly overhead an Earth-based measuring device. Earth-based upward-looking water vapor radiometers estimate PWV by measuring radiative brightness temperatures against the cold background of space. However, upward-looking water vapor radiometers must be “tuned” to local conditions using independently obtained PWV data, and although they generally exhibit good temporal resolution in relatively clear atmospheric conditions, they provide only localized PWV over land. Further, unless properly equipped, upward-looking radiometers are virtually useless in rain. Alternatively, satellite-based, downward-looking radiometers perform well over water and consistent temperature land masses by viewing microwave emissions from the atmosphere and underlying Earth's surface. Although downward-looking radiometers generally exhibit good spatial resolution they exhibit poor temporal resolution and perform poorly over most land masses. In either case, water vapor radiometers as a whole are not practical for global scale meteorology due to their cost, limited view, and performance characteristics.
Fourier Transform Infrared Radiometer (FTIR) systems can provide high resolution satellite-based and Earth-based temperature and water vapor profiles by using a recursive solution of the radiative transfer equation to provide a vertical profile from the ground up. Although this method can provide vertical resolution of several hundred meters to a kilometer in the lower troposphere, the system exhibits poor performance in the presence of cloud cover and infrared active gases such as tropospheric ozone.
Unmanned Air Vehicles (UAV's) provide high resolution data in regions inaccessible to other systems discussed above. However, unmanned aircraft are too costly for continuous global sensing, they lack adequate spatial and temporal resolution, and are typically only justified in specialized research applications.
Additional water content measurements are available from satellites and from a few specially-equipped airliners operated under a NASA program called Tropospheric Airborne Meteorological Data Reporting (TAMDAR). Satellite data are unreliable because it is difficult for satellites to correctly resolve the altitude profile of moisture, especially when clouds are present. TAMDAR uses humidity sensors mounted on the outside of small, regional airliners. These sensors continuously measure humidity and temperature as the aircraft ascend and descend through the troposphere. This provides better spatial and temporal resolution than radiosondes. Though this approach has been shown to be technically effective for improved weather forecasts in the northeastern US, the additional weight and drag and the need for FAA certification of each type of sensor package on each type of aircraft makes this solution costly, which has limited the expansion of existing systems to other regions.